Sound file formats

A sound file is an individual sound recording of any length, whose individual parts may or may not have been recorded at different times. With analogue reel-to-reel tape, these recordings will be separated by leader tape, and may be album tracks, takes from a studio session or short sound effects. Similarly, digitally recorded sounds are stored as sound files of different lengths, but one advantage over analogue storage is that the random- and direct-access nature of the storage medium means that one individual sound file has no specific time relationship to another. Older recordings will be found nearer the start of an analogue reel, but this is not the case with digital recordings, since digital audio is stored non-linearly.

During the late 1970s and early 80s, several sites developed UNIX-based sound file systems for the benefit of storing computer music. The formats were generally different to the standard UNIX file system and so required separate disks (or disk partitions) for sound storage.

The root of most research into audio file formats is the csound file system, which first appeared in 1980, and was developed by D. Gareth Loy at the Computer Research Lab (CARL) at UC San Diego. CARL music software distribution contained various tools such as vocoders, configurable reverberators, as well as software such as Csound and the cmusic scripting language (a simple C-based language descended from the Music V language, and written by F Richard Moore).

In the late 1980s, the several variations of software based on csound were merged into the BICSF (Berkeley/IRCAM /CARL Sound File) System and adapted to allow compatibility and interoperability with other computer systems such as NeXt and SPARC.

A standard digital audio file is recognised by its .au extension, and unlike many computer files, is platform-independent, which means that it can be read by any computer with the appropriate software. The main disadvantage of digital audio files is that they consume the largest amount of disk space since they comprise of pure PCM (Pulse Code Modulation), i.e. raw digital data, which makes them the least appropriate format for delivering audio across the Internet.

AIFF/WAV

In 1988, Apple Computers published "AIFF (Audio Interchange File Format): A Standard For Sampled Sound Files" - a document detailing a sound file format developed by Apple for storing digital audio. The format stores both monaural and multi-channel sampled sounds, at a variety of sample rates and bandwidths.

Audio IFF was originally developed as an interchange format; i.e. to encode data into a specific language, but it was also used as a storage format for audio data. It was recommended in the document that should audio application designers choose to use a different storage format, that the chosen format should be able to convert to and from the AIFF format developed by Apple. This allowed easier sharing of data between various audio applications for the Macintosh .[5]

AIFF was intended for use with a wide range of computers, sampled sound instruments, sound software applications and hi-fi recording devices. The format has become one of the most common audio files for the Mac, and is recognised by most, if not all, sound editing and hard disk recording software such as ProTools and Sound Designer.

The WaveForm Audio File Format, also known as RIFF WAVE format, is a Microsoft Windows 3.1 sound standard. As with AIFF, WAVE files are sound data files - digital representations of analogue sounds, but are compatible with IBM PCs rather than Apple Macintosh, and are recognised by their .wav extension. Also similar to the AIFF format, is WAVE's compatibility with various software for the PC, from sound editors and hard disk recorders, to games and even sounds within word-processed presentation documents.

mpeg audio (mp3)

Though AIFF and WAV files are smaller in size than .au files, they are still too large to be transported comfortably over the Internet, because of the vast amounts of data they hold. One method of saving storage space and of speeding up Internet download times was the development of the MPEG (Moving Pictures Experts Group) Audio compressed digital sound file.

MPEG is a subcommittee of ISO/IEC (the International Standards Organisation / International Electrotechnical Commission) who define standards for digital audio and video compression, and MPEG Audio is the audio part of the compressed MPEG audio/visual signal, which can be used in conjunction with, or independently of, a visual signal.[6]